Process for the preparation of monochromates and dichromates



Y dium, .the quantity ofthe alkaline agent employed' Ybeing such thatAfor thercase of the formationriof f dihromates it remains below thatrequired for Patented ug. 20 1935 PROCESS lion 2,012,062 j THE.PREPARATION 0F MONOCHROMATES AND DICHROMATES Jules Emilel Dezinant,CuiseLamotte,1Franoe, aS'- 'signor to Bezel-Malena, Socit Industrielledev Produits ChimiquesgjP tion yof France chromates and diohromates, f;

I have..` already vproposed, inmy Pate-nt Nol,A 1,955,326dated YAprilr17, 1934,1a process` forthe manufacture of monochromates .andYdichromates consistingl in subjectingat temperatures above 10020.,metallic chromium or substances .con.

tainingV the same orv chromium alloys to an oxidizingl reaction in thepresence cfgalkaline-.oi1

alkaline earth hydroxides,carbonates, onbicarbonates or of Ymonochromates an aqueousmethe iormation; of monochromates.Y i I l MInacoordance With u the Ypresent invention it Vhas been found that forlthe formation of mono'- chnomates or dichromates Vthelpresence of`alka.- t

lineeor-` alkalineearth .hydroxides carloonateav or bicagrbonatesY oroffmonochromates is not abso-Y lutjely nece ss.ary. Y .Inaocordanoe withtheinventionfit isV possiblerfifo employ;` instead of or gtogiherfwithalkaline-oLalkaline earth agents and, in the case of the preparationof.dici-1romates, instead ofor together with alkaline-or alkaline .eartl1:agents-,orof Vmonochromates, in

general allcompoundslcapahle of giving up Ytheir] alkaline principlelinden-the oxidizing actionl in.

the course of the 'DIOCssi i By suchfoxidizing conditionsl itis Vto be.un-V derstoodas disclosed by the examples given inj this speciicationlater on, that the reaction takes place with a current-,of oxygen Aorairunder arti;-

Aiicial pressure. or W-ith oxygen developed during the reactionthroughgithe initial introduction Vof an oxygen-yielding, reagent likepotassium* chlorateL f "Ilie tendency of chromium to beconverted in-tohexayalentchrornium is so Vmarked that in the course of the oxidizingprocessgzthe added sub'- stances undergo va-decomposition which causes ithem .to give .up theirn alkalineprinciple tothe`.chron-iiurrl;according to the quantity of the alkaline piincipleentering into reaction it is'rpossible to obtain either monochromatesordichromates ormixtures of these twocompounds. Y

.In order' to properly.y distinguish between, an falkaline agentperse.and a substance which in v.thisLeaseunderproper oxidizing conditionswill give up its falkaline principle to the chromium, it -iswell toremember that: i'.

A Solution LofY anacidcontains -catonwH and Y*non-metall-ic ions(anions) Va sol lotion .of a .base contains hydroxylions V(an-ions)v andmetallic ions (.c'aticms);V and a solution of a hydrogen `ions Yarisg-France, a. corpora,-

s clanes; l' (c1: 23.-5s1) saItcOntanS non-.metallic (anions) and 1011satioiis). t I v l VIn an .acid the anionsare'the .active elementsWhichcombine with the' attacked metal, forming chlorides,sulphatesphcsphates, nitrates, ete,

freeing the lfiydrogeri.` In .a base .01T alkaline agent, it is theoationfwhioh -ifs'the.:actiye.ellesA ment, While in asalt solution'theanions and i cations' `lflirili'arid neutralize .leach other, as long`asnodecomposition takesplace, .Only l.

after .suon decomposition is effected under .special I-cireumstances,tree` acting cations are .liberatori and-a chemical reaction isjrealizedThus asap stance `vviiricli .normallyY cannot be' f classified .as base,.can becomean alkaline' agent.

While an alkaline agent contains itsationjn Ldo not .claim .as nari .ofmy inv.antiontheV .use of..oxides,.hydroxides .oi :alkali .or .alkaliearth metals'per senfNor `.dojrI Lclz'tim't'hz-e use yo`:f2..cnl2+bonates oi alkali .oi-alkali .earth metals per se.'

Ido not claim as part ofmy presentinvention aireerstatathe substances,employed according to fthe present invention Vare kthose capable .of 1liberating their `cations...generally under th.. #i dizing :action .ofthe reaction.'

Vthe yuse .of monochromates, taken alone, sub-1 stances capable ofgivin'gfupfree acting' cations to the 4chromium under the' influence offthe' .oxi-

' dizing reaction,

As compounds Whichv i in themselves are-" base Vbut in the presence ofari-oxidizing reaction are capable of giving up their alkalineprinci-ple',

'tl-ierecan vloe employed the most'varied salts of vstrong or Weakinorganic or'orga-nic acid'sor-also oxygen compounds of a salt likeCharacteLQOr i chlorides, phosphates, monochromatesgvaoetates,silicates, aluminates, nitrates, chlorates, nthefper salts, manganates,permanganates o r-t'he like@ It may be remarked that theselat-tercompounds can actbothas oxidizing Vagents and when decomposed jasalkaline agents, :They can even be utilized oniyias oxidizing .agentstogether with true alkalinagents'or other agents" capable 'of Agiving'up their; alkaline principle. As alkaline agents are` usedlalkaline `0ralkaline earthhysiroxidea .Carbonates' or .bicarbonates ormonochromates..

-uptneir cations under the action .of the' 'oxidizing reaction.4 Saidcharacteristic is clearly exem- Plifled by ihefollowing Examples 1;2,',and 43.. N

lffor example organic derivativeslarevveme ployed, ithe onganic.principleis in general oxidized As amatter .of fact, Y.the s311135 just.bOV indicati@ are Vnormally not bases biliare .Capable .of sittinglowing examples are given and it may be remarked that Example 5illustrates the splitting up of potassium sulphate under the oxidizing-decomposition action of trivalent chromium.

Examples (l) 16 parts of finely pulverized errochrome-y containing 65%Cr and 9.5% C, :14.2 parts of anhydrous sodium sulphate, 10 parts ofcalcium carbonate, 200 parts of Water are heated in an autoclave Withgood agitation at Zim-290 C.; a current of oxygen or air is passedthrough under pressure. The progress of the reaction is controlled bymeans of the content'of carbonic acid which is determined in the gasleaving the apparatus.

` The reaction product is filtered. The liquid contains pureV sodiumdichromate.

V`iZield97%. f 1 -(2) 16 parts of nely pulverizedV ferrochromecontaining 65% Cr and 9.5% C, 28.4 parts of anhydrous sodium sulphate,20 partsof calcium Vcarbonate, 200 parts of Water are treated asindicated in Examplel.

v After filtration of the reaction product a-liquid lis obtainedcontaining sodiumjmonochromate. 4Yield quantitative. f o f y `(3) 16parts of finely pulverized ferrochrome 200 parts of water, are heated inan autoclave for some-hoursto`290-300 C. VvTowards the end of'the'reaction alittle oxygenV under pressure is passed through in ordertofacilitatethe elimination of 'carbonic acid formed and to support theoxidation.`` l

There are easily obtained yields of potassium dichromateexceeding '70%.1 n y.

. (4) 16 ,parts of finely pulverized ferrochrome containing 65% Cr and9.5% C, 139 parts of trisodium phosphate l Aq, 200 parts of Water, areheated in an autoclave with good agitation for some hours to 280-1300oC. and a Acurrent of air or oxygen is passed through Withathepracticallycomplete elimination of` the carbonio acid produced-.fromrtheferrochrome. There is obtained afteriltration a monochromatic liquortogether with disodiumphosphate which is separatedby crystallization.Yield about 80%.

p (5) y17.3 parts of ferrochrome of 60% Cr, 35 parts of potassiumsulphate, 200 parts of vvvater are heated for some hours in a current ofoxygen at 280-300 C. in an autoclave with gooda'gitation. The reactionproduct is iiltered and there is obtained an acid liquid containingpotassium dichromato. phate has produced alkali which is absorbed by thehexavalent chromium on one hand and the =:free sulphuric acid on theother'hand.

` Thefree acid present prevents the reaction from progressing beyondacontent of free acid of rabout 0.5% H2504.'

The yield obtained is 16-20% for the above example. n By Working in amore dilute medium in such a The splitting up of the potassium sulmanneras to remain below a content of free acid of 0.5% H2SO4 the yield can beconsiderably increased. In this case it is desirable to increase thecontent of potassium sulphate.

This'method of working presents the inconvenience of producing aciddichromate liquors of loW contentand by reason ofV this fact it is to berecommended to neutralize the free acid formed during the reactionpreferably by adding f1. Process for Ythe manufacture of monochromatesor dichromates consisting in subjecting a substance containing metallicchromium to oxidizing decomposition at temperatures above 100 C.,underpressure and in an aqueous medium, in the presence of a compoundbeing not normally classiied as a base but other than a monochromate andcapable of giving up free acting cations to the chromium under theinfluence of the oxidizing reaction. v v2. Process for the manufactureof monochromatesor dichromates consisting in subjecting a substancecontaining metallic chromium to oxidizingdecomposition at temperaturesabove 100 C., under pressure and in an aqueous medium, in the presenceof a compound being not normally classied as a base but other than amonochromate and-capable of giving up free Aacting cations to thechromium under the influence of the oxidizing reaction, and in thepresence of an alkaline agent. o

l3.'Prooess for the manufacture of- Vmonochromates or dichromatesconsisting in subjecting a substance containingmetallic chromium tooxidizing decomposition at tenriperatures above `100" C., under pressureand in an aqueous medium, in the presence of a compound being notnormally classied as a base but other than a mono- Ychromate andycapable of giving up free acting cations to the chromium under theiniluence of the oxidizing reaction, and acting at the same time as anoxidizing agent. Y

4'. Process Vfor the manufacture' of monoohromates or dichromatesconsisting in subject- Y ing a substance containingvmetallic chromium tooxidizing decomposition at 'temperatures' above 100 C., under pressureand in an aqueous medium, in the presence of `a compound rbeing notnormally classied as a base but other than a monochromate'and'capable ofgiving up free acting cations tothe chromium under the influence of theoxidizing reaction, and acting at the same time as an oxidizing agentand in the presence of an alkaline agent. Y v I 5. Process for themanufacture of `monochromates ordichromatesconsisting in subjectingferrochrome to oxidizing decomposition at temperatures above 100 C.,under pressure and in an aqueous medium in the presence of a compoundbeing not normally classied as a base but other than a'monochromate andcapable of giving up free acting cations to the chromium under the lin-`iiuence of the oxidizing reaction. f 6. Process Afor the manufacture ofmono chromates or dichromates consisting in subjecting ferrochrome tooxidizing decomposition at temperatures above 100 C., under pressure andinv 'an aqueous medium,`in the presence of a coman aqueous medium, inthe presence of Y a compound being not normaliy'classiiied as a base butother than a monochromate and capable of giv-v ing up free actingcations to the chromium under the inuence of the. oxidizing reaction,and acting at the same time as an oxidizing agent. l

8. Process for the manufacture of monochromates or 'dichromatesconsisting in .subjecting ferrochrome to oxidizing decomposition attemperatures above 100 C., under pressure and inA f an aqueous medium,inthe presence of a compound being not normallyclassied as a base butother than a monochromate and capable Aof giving up free vactingcatior'lsr to the chromium under the influence of the oxidizingreaction, and act- K ing at the saine time as'an oxidizing agent and inthe presence of ran alkaline agent.

JULES EmLE DEMANT.

